Apparatus for ultrasonic determination of surface structures and subsurface structures of an object is described in DE OS 40 16 105 A1 which corresponds in part to U.S. Pat. No. 5,258,922. This apparatus permits an object placed upon a planar or domed support which is transmissive to ultrasonic waves to be determined by transmitting the ultrasonic waves through a liquid or a solid body onto the object, and detecting the ultrasonic waves which are backscattered and reflected from that object.
From the intensity of the backscattered surface, characteristics of the surface of the object and subsurface or surface-adjacent structures can be determined. The transmitter of the ultrasonic waves and the receiver are disk-shaped and separate from one another. The transmitter in this system had to be designed to produce planar or spherical waves parallel to the surface and the receiver could only be one which was sensitive to such waves. In this manner the receiver effected directly a Fourier transformation from which respective parameters of the received waves, like phase amplitude or intensity, could be derived. Depending upon the structure of the object subjected to the ultrasonic waves, the scattering and hence the intensity of the backscattered waves in the different direction can strongly differ. From the intensity values measured results like numerical values, color displacement or the like can be generated which reflects the surface pattern of the object for use in, for example, identification.
While this system has been found to be largely satisfactory, experience with it has shown that the results were highly dependent on the positioning of the object on the support.